Solar uv transmissive device for sterilizing and/or heating air

ABSTRACT

An outdoor air conduit or plenum is provided with a UV transmissive surface for allowing the air circulated through the conduit to be exposed to the UV rays of the natural sunlight, thereby providing for the sterilization of the air using free energy. The air sterilization system can be integrated to a building ventilation system or combined with a solar heat collector.

TECHNICAL FIELD

The present application generally relates to a device and a method suited for sterilizing and/or heating air by means of free energy, such as solar energy. For instance, the device can be used for heating and sterilizing the air of a building.

BACKGROUND ART The Sterilizing Effect of UV Rays

Ultraviolet rays (UV rays) are known to have a purifying effect on water as well as on air.

In closed systems, the re-circulated building air accumulates pathogeneous organisms that may generate diseases. Among the various types of UV rays, the UV-C rays are known to inhibit the growth and the reproducing of germs, viruses, allergies and bacteria's that circulate in warm or cold air ducts systems.

Over the years various UV rays generators have been developed in an attempt to process and purify air in a given environment. While it is known that solar radiation contains UV rays that have a sterilizing effect, there is, according to applicant's knowledge, no device currently on the market which makes active use of the benefits or solar energy to sterilize the air. There is a need to take advantage of solar radiation in the duct systems to further increase the effectiveness of existing UV ray systems.

Solar Collectors and UV Rays

Design of traditional glazed solar air heaters generally comprises a glass or transparent cover placed in front of a dark solar absorber. The front transparent cover is provided for minimizing heat losses from the top of the collector. Fresh outside air is traditionally admitted at one end of the collector between the solar absorber and the insulated bottom of the collector. The air passes through the collector along tins and absorbs heat from under the solar absorber as it travels therealong. Warm or hot air is discharged at the opposite extremity of the collector. As air progresses inside the collector, its temperature rises above ambient. The higher the temperature in the collector is, the higher the heat loss towards the ambient becomes. Heat loss happens through the bottom, the edges and the top (where the glazing is) of the collector. Typically the edges and the bottom are insulated, so that heat loss mostly occurs through the top, that is by convection between the absorber and the glazing and then by conduction through the glazing. When the glazing becomes very warm, the collectors become less efficient.

Various unglazed solar air heaters have also been designed over the years. Current transpired collector designs are such that the solar absorbing surface is located outside facing the sun, unprotected by means of a glazing. The perforated absorber is coupled to a fan which creates a negative pressure between the building (or the bottom of the collector) and the absorber. When the fan is in operation, the air is drawn through the absorber. The air passing through the perforations in the outer opaque absorber breaks the naturally occurring warm film of air on the outside facing side (the boundary layer) of the absorber. This method provides acceptable performances when the flow of air per unit area exceeds 6 cfm per square foot of collector. However, for unitary flow rates below 5 cfm per square foot, the amount of cool air leaching the perforated plate is insufficient to prevent the collector plate from heating up, thereby negatively affecting the overall thermal efficiency of the system. Efficiencies at the rate of 2 cfm per square foot drop to 30% or even less.

The air circulating under or behind the absorbers never “sees” sunlight and therefore the sterilizing properties of the sun are not being put to advantage. Furthermore, traditional glass used as top glazing is not transparent to the sun's UV rays, therefore the heated air never gets the sterilizing benefits of the sun's UV rays.

In view of the foregoing, there is a need for a relatively low maintenance and simple solar energy based device that can be used to sterilize and/or heat air.

SUMMARY

It is therefore an aim to address the above mentioned issues.

According to one general aspect of the present application, there is provided a solar heat collector which also provides for air sterilization by allowing the incoming UV rays to irradiate the air passing behind or under a UV transmissive surface.

In accordance with another general aspect of the present application, there is provided a heat collector and air sterilization device comprising a UV transmissive glazing exposed to the ambient, the UV transmissive glazing allowing at least a portion of the UV rays of the sunlight to pass therethrough, the UV transmissive glazing being spaced from a back surface to define a plenum therewith, a plurality of perforations defined through the UV transmissive glazing for allowing outside air to flow through the transparent glazing into the plenum, the perforations being distributed over a surface area of the UV transmissive glazing, the plenum having at least one outlet through which air contained in the plenum can be removed after having been warmed up and at least partly sterilized by the UV rays of the sunlight. The back surface can be provided in the form of a solar radiation absorbing panel or the like.

In accordance with another general aspect, there is provided a device for heating and sterilizing air comprising a perforated UV transmissive surface allowing at least part of the solar radiations, including UV rays, to pass therethrough, a solar radiation absorption surface located behind said perforated UV transmissive surface for absorbing the solar radiations, and a plenum defined between said perforated UV transmissive surface and said radiation absorption surface, the air flowing in the plenum absorbing heat from the radiation absorption surface while being exposed to UV rays, thereby providing for the combined heating and sterilization of the air in the plenum by solar energy. The perforations in the UV transmissive surface provides for a reduced temperature delta through the UV transmissive surface, thereby ensuring a better heat transfer efficiency.

In accordance with still another general aspect, there is provided an outdoor transparent and perforated surface exposed to the ambient. The perforated transparent surface is permeable to UV rays and spaced from a back surface so as to define an air gap or plenum therebetween. Fresh outside air is drawn into the plenum through the perforated transparent surface. The back surface can, for instance, be provided in the form of a bottom of a solar collector, a building wall or roof, an outer surface of a greenhouse, a photovoltaic panel, a ground surface or any non-porous surface. Between the perforated transparent surface and the back surface, the gap of air is maintained under negative pressure due to mechanical or natural means. An outlet is provided for allowing air flowing through the plenum to be drawn into a duct or a channel, for use as make-up, ventilation, process or combustion air to a device which consumes or needs thermal energy. As the air travels along the plenum it is being purified under the action of the UV rays passing through the perforated transparent surface.

The air in the plenum can be heated either by incident solar radiation on the surface of the back panel, which acts as a solar absorber, and/or by heat escaping from the back surface. The device can therefore act as a solar air heater and/or as a heat recovery unit and/or as a sterilization unit. When used as a solar air heater, the back surface can be of a dark color, so that incident solar radiation passing through the perforated transparent surface is absorbed by the back surface in the form of heat and not reflected back to outer space. However, if the back surface, for any aesthetic reason or other, must be of light color, the solar thermal efficiency remains higher than other conventional unglazed collector design. This is particularly true when the device is used as a heat recovery device, since the back surface can be of any color with substantially no influence on efficiency (it can even be transparent like in the case of a greenhouse), but the lower the thermal resistance (insulation) of the back surface, the greater the heat recovery rate. The device can be simultaneously used for all three functions of solar heating, heat recovery and UV sterilization.

It is understood that in warmer climates, the back panel or surface may event be of white color, of reflective surface or even transparent if no solar heat gain is necessary.

If necessary, the preheated air leaving the device can have an auxiliary heating device located downstream (e.g. a gas-fired system) to bring its temperature to a given set point.

If necessary, the at least partially sterilized air leaving the device can be further processed by an auxiliary air sterilizing device (e.g. a UV-C generator system or chemical based purifying system) located downstream of the outlet of the outdoor plenum to further purify the air to a given set point.

In accordance with a still further general aspect, there is provided an outdoor system for sterilizing the air of a building, the outdoor system comprising:

-   -   at least one air sterilization device mounted outside of the         building; the device comprising a plenum having a UV         transmissive surface exposed to sun rays, the UV transmissive         surface allowing at least part of the UV rays of the sun to pass         therethrough in order to sterilize the air in the plenum,     -   the plenum having at least one inlet feed with air from the         building; and     -   at least one outlet feeding the building with sterilized air         from the plenum.

The system for sterilizing the air of a building may further comprise: at least one auxiliary sterilization device that can be disposed downstream of the air sterilization device in order to further sterilize the air before the same be returned back into the building. The auxiliary sterilization device could for instance take the form of a UV ray generator, a chemical sterilization device or a photocatalyst device.

A controller could be provided for selectively actuating the auxiliary sterilizing device. For instance, the controller could be programmed or otherwise configured to actuate the auxiliary sterilization device for producing additional UV rays during the night or by covered weather. Suitable sensors could be connected t o the controller to provide feedback on the quality of the air and the intensity of the sun rays.

According to an embodiment, the system for sterilizing the air of a building can comprise at least two auxiliary sterilization devices mounted in parallel or in series.

In accordance with a still general aspect, the system can also be used to pre-heat the air before returning the same into the building. This can be accomplished by providing a solar radiation panel behind the UV transmissive cover of the plenum. Also, if an income of fresh outside air is desired, the UV transmissive cover can be perforated to allow fresh outside air to flow into the plenum and mix with the recirculation air of the building.

The air sterilization device of the system can take the form of an outdoor conduit connected to the ventilation system of the building. In this example, at least a portion of the conduit would be transparent to UV rays to allow the air flowing through the conduit to be exposed to the UV rays of the sun while flowing through the conduit.

The roof mounted conduit may comprise a plurality of duct sections adapted to be connected end to end in fluid flow communication to form a fluid passage for allowing air to flow therethrough. At least some of the plurality of duct sections could be provided with a ballast receiving portion, and a ballast material could be placed on said ballast receiving portion for anchoring the duct sections to a flat roof under the weight of the ballast material. The duct sections and the ballast material would have a combined weight selected to render the duct sections substantially immovable to side winds on the flat roof of the building.

According to a still further general aspect of the application, there is provided a method for heating and sterilizing air, the method comprises directing air to be processed into a plenum having a UV transparent surface, exposing air through said UV transparent surface to UV rays of the sun, absorbing at least a portion of the sun rays passing through said UV transparent surface onto a solar radiation absorbing surface located behind said UV transparent surface, and heating the air in the plenum with the solar radiation absorbed by said solar radiation absorbing surface.

According to a still further general aspect, there is provided a process for building a heat and sterilization device according to anyone of claims 1 to 16 comprising the step of assembling the different constituting elements of the device. The assembly can be done through the used of any suitable methods including welding, fitting, bolting and/or screwing.

According to a still further general aspect, the system for sterilizing the air of a building can be used for disinfecting buildings such as hospital, school, grocery stores, office towers, medical practices, waiting rooms etc. This can contribute to substantially reduce the amount of disinfecting compounds such as biocides, fungicides, bactericides and antibiotics injected in the air circulating in such buildings.

According to a still further general aspect, there is provided a process for heating and at least partially disinfecting a contaminated air source, which process comprises circulating the contaminated air at least one time through at least one sterilization device as generally defined hereinabove.

The term “glazing” is herein intended to broadly refer to any transparent surface allowing the light to pass therethrough.

The terms “UV transparent” and “UV transmissive” are herein intended to refer to a surface which allows sunlight to pass through without substantially blocking the UV rays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a solar collector including a perforated transparent surface in accordance with an embodiment of the present invention;

FIG. 2 is a schematic side view of another embodiment of a solar collector having a perforated transparent glazing;

FIGS. 3 and 4 are schematic side views of ground-mount configurations of solar collectors having perforated transparent glazing in accordance with further embodiments of the present invention;

FIG. 5 is a schematic side view of a wall mounted solar collector having a perforated transparent glazing;

FIG. 6 is a schematic side view of a roof mounted solar collector having a perforated transparent glazing;

FIG. 7 is a schematic view illustrating a perforated transparent glazing surrounding a greenhouse shell for pre-heating cold outside air before being drawn into the greenhouse by a ventilation system;

FIG. 8 is a graphic comparing the efficiency of perforated glazing collectors vs. unglazed perforated collectors as a function of the quantity of air flowing therethrough;

FIG. 9 is a schematic view of a system for heating and sterilizing the air of a building, according to one embodiment of the present invention, mounted on the building surface;

FIG. 10 is a schematic view of a system for heating and sterilizing the air of a building, according to an embodiment of the invention, comprising an air collector mounted separately from the building; and

FIG. 11 is a graphic illustrating the UV transmittance of S1-UV Ultraviolet Grade Fused Silica manufactured by the company ESco Products as a function of the Wavelength of the light.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a solar air heater 10 provided in the form of an elongated conduit-like enclosure mounted on a base and including a sun facing perforated transparent glazing 12 exposed to the ambient and placed in front of a back panel having an arcuate solar radiation absorber plate 14 applied over an insulation layer 15. The back panel is generally provided in the form of a half-pipe wall covered with the perforated transparent glazing 12. The absorber plate 14 can be of a dark color to maximize solar gain. The perforated glazing 12 can be provided in the form of a perforated polycarbonate or transparent UV-resistant plate. Other transparent polymers could be used as well. As will be seen hereinafter, the glazing 12 can be selected so as to be transparent or permeable to UV rays in order to also provide for UV rays sterilization of the air flowing through the conduit-like enclosure. This is advantageous in that it allows to simultaneously pre-heat and at least partly sterilized the air using solar energy. The glazing 12 can be rigid or flexible. The perforations can be distributed over the entire surface of the glazing or over only a selected surface area thereof. The density of perforations can be uniform or variable over the glazing surface.

The perforated glazing 12 and the solar radiation absorber plate 14 define a plenum 16 therebetween. A fan or other suitable air moving means 17 can operatively connected to an outlet 18 provided at one end of the back panel to draw fresh outside air through the perforated glazing 12 into the plenum 16 before being directed to a ventilation system, such as a building ventilation system. The solar radiations passing through the perforated transparent glazing 12 are absorbed by the absorber plate 14. The air in the plenum 16 picks up the heat absorbed by the absorber plate 14 before being drawn out of the plenum 16. As air travels longitudinally along the plenum 16 between the absorber plate 14 and the perforated glazing 12, additional fresh outside air is drawn through the perforated glazing 12. In this way, the glazing 12 remains at a temperature substantially equal to the ambient temperature. Accordingly, the temperature differential between the incoming air and the ambient is equal to zero or close to zero, so that thermal efficiency remains at the highest possible value. Heat losses through the glazing cover are thus kept to a minimum.

FIG. 2 shows a second embodiment in which like reference characters refer to like components. The solar air heater 10 a shown in FIG. 2 essentially differs from the solar air heater 10 shown in FIG. 1 in that the solar air heater 10 a has a planar configuration characterized by spaced-apart parallel transparent glazing and back panel. The back panel is provided in the form of a flat absorber plate 14 a applied over a planar layer of insulation material 15 a. The absorber plate 14 a could be corrugated. Sidewalls or supports 19 a are provided along the perimeter of the back panel and the perforated transparent glazing 12 a in order to create a uniform air gap 16 a therebetween. The perforated glazing 12 a and the back panel are preferably co-extensive. The back panel 14 a can be provided in the form of photovoltaic (PV) panels to provide the double function of air heating and cooling the PV panels, which produce more electricity when their surface is kept at cool temperatures. As shown in FIGS. 1 and 2, the perforated transparent glazing 12 a is preferably supported at an inclination equal to the latitude of a given location, and facing the equator, depending on use. However, it is understood that the transparent glazing could be oriented and inclined otherwise. For instance, FIG. 4 shows a horizontally oriented perforated transparent glazing, whereas FIG. 5 shows a vertically oriented glazing.

As shown in FIGS. 3 and 4, the solar air heater can be mounted directly on the ground, the ground surface forming the back panel of the device. In the embodiment of FIG. 3, wherein like reference characters refer to like components, the plenum 16 b is formed by the perforated transparent glazing 12 b, a building wall 20 b and the ground G. The fresh outside air drawn in the plenum 16 b is heated by the solar radiations absorbed by the ground G as well as by the heat escaping from the building through wall 20 b. The fresh outside air flowing through the perforations defined in the transparent glazing 12 b maintains the temperature delta across the glazing close to zero, thereby ensuring high thermal efficiency. The heated air is drawn out from the plenum 16 b and circulated in the building B via the building ventilation system (not shown). As shown in FIG. 4, where like reference characters again refer to like components, the solar air heater can also be provided in the form of an enclosure having a perimeter wall 19 c, a closed bottom end formed by the ground, and a top end covered by the perforated transparent glazing 12 c. An outlet 18 c connected to suitable air moving means is provided for withdrawing the heated air from the enclosure.

As shown in FIGS. 5 and 6, the perforated transparent glazing 12 d and 12 e can be mounted in opposed facing relationship to a building wall 20 d or the roof 22 e of a building. In the embodiment of FIG. 5, the plenum 16 d is formed between the outside surface of the building wall 20 d and the adjacent vertically oriented perforated transparent glazing 12 d. In the embodiment of FIG. 6, the plenum 16 e is formed by the outside surface of the building roof 22 e and the perforated transparent glazing 12 e. In both embodiments, the heat escaping from the building envelope through the wall 20 d or the roof 22 e is recovered to heat the air in the plenum 16 d and 16 e. The roof 22 e and the building wall 20 d both act as solar radiation absorbers to further heat the ambient air drawn in the plenums 16 d and 16 e. The solar radiations pass through the perforated transparent glazing and are absorbed by the underlying building wall or roof surfaces and the air in the plenum absorbs the heat from the building wall or roof. As opposed to conventional solar walls or solar roofs wherein solar radiation are directly absorbed by dark panels covering the wall or roof of the buildings, the transparent glazing does not negatively alter the appearance (i.e. change the color of the building wall or roof) of the building. Unlike the prior art, the performance of the system is not influence or restricted by the color of perforated panels installed on the building wall or roof. The perforated glazing 12 d and 12 e are transparent and thus they do not change the color of the building wall or roof. No compromise has to be done for aesthetic purposes.

FIG. 7 shows a further potential application of the present invention. More particularly, FIG. 7 illustrates a greenhouse B′ having a skeleton framework covered with a transparent skin 25 f or membrane, as well know in the art. A perforated transparent glazing 12 f is mounted to the greenhouse wall and roof to define a double-walled structure including an air gap 16 f defined between the perforated transparent glazing 12 f and the inner transparent skin 25. In this embodiment, the perforated transparent glazing 12 f acts as a second insulation layer for the greenhouse B′. The heat escaping from the greenhouse through the inner skin 25 is recovered in the air gap 16 f. A fan or the like can be provided for drawing heated air from the air gap back into the greenhouse B′. The perforated transparent glazing 12 f maintains the required transparency required for plant growth.

As mentioned hereinbefore, the sun facing glazing 12 of the various embodiments of the heat collector illustrated in FIGS. 1 to 7 can advantageously be made of a UV transmissive material to take benefit of the purifying or sterilization properties of the UV rays on the air. The exposition of the air to the UV rays of the sun in the plenum allows sterilizing the air while the same is being heated up in the plenum.

The UV transmissive glazing is preferably made of a material selected from the group consisting of: polycarbonates and fused silicae. The UV transmissive glazing could, for instance, be made of fused silicate offered by the company ESco Products.

Particularly recommended for use as the sun facing glazing 12 of the above described embodiments of the solar air heater are S1-UV Ultraviolet Grade Fused Silica, Grades A and B of the ESco Products company. As shown in FIG. 11, such materials have an optimum transmission range (more than 90% UV transmissive) for wavelength comprised between 180 nm-2.0 μm and are thus excellent UV transmitters.

Such pure fused silica materials offer good transmittance down into the deep UV. They provide great homogeneity making them ideal for applications demanding superior wavefront performance. As fused silica materials, they show no fluorescence or discoloration when exposed to radiation shorter than 290 nm. S1-UVA has slightly better homogeneity and fewer and smaller bubbles than S1-UVB.

Other materials that are permeable to UV rays of the C-type, and having a UV transmittance rate that is higher than 80%, and preferably higher than 85%, more preferably higher than 90% are contemplated as well.

FIG. 9 illustrates one possible embodiment of a combined solar air heater and air sterilization device 29. The air heater and sterilization device 29 comprises an outdoor UV transmissive panel 12′ mounted on a sun facing wall 20′ of a building and defining therewith a plenum 16′, As illustrated, the UV transmissive panel 12′ can be perforated to allow fresh outside air to flow into the plenum 16′. The building wall 20′ can be made of a dark color to absorb solar energy. An outlet is provided at the upper end portion of the plenum 16′ for allowing heated and UV sterilized air to be drawn from the plenum 16′ into a ventilation conduit 35′ of the building by operation of a fan 32. An auxiliary UV generator 33 can be disposed between the plenum outlet and the building ventilation conduit 35 to provide additional air purification before the air be directed into the building ventilation system. The auxiliary UV generator 33 is operated by a controller 30 which is in turn operatively connected to a light intensity sensor 31 and first and second air quality sensor 37, 36. The sensor 31 is disposed to measure the intensity of the incident sun rays on the UV transparent panel 12′. The first and second air quality sensors 37 and 36 are respectively disposed at the exit of the plenum 16′ and at the exit of the auxiliary UV generator 33 for measuring the quality of the air being fed to the building ventilation system. In operation, the controller 30 receives signals from the solar radiation sensor 31 and from the first air quality sensor 37, positioned upstream to the ventilator 32. If the quality of the air flowing out of the UV exposed plenum is not as good as desired, a signal is sent from the controller 30 to the UV generator 33 for producing the amount of artificial UV rays necessary for reaching the desired purity value. The sensor 36 measures the purity of the air feeding the building 35 and provides feedback to the controller to determine whether a control command should be send to the auxiliary UV generator to produce more or less UV rays. The controller can also be connected to the fan 32 to adjust the residence time or UV exposure time of the air in the plenum as a function of the intensity of the sunlight.

The residence time of the air in the plenum behind the UV transmissive glazing 12 can be lower or equal to about 5 minutes and preferably no longer than about 1 minute. However, the air must be exposed to the sun UV rays for a sufficient period of time in order for the sterilization process to occur. The residence or UV exposed time will vary depending on the intensity of the sun rays and the mass flow of air in the plenum 16′.

According to one example, the auxiliary UV generator 33 is:

-   -   a) deactivated when the intensity of the solar exposition on the         site as detected by sensor 31 is greater than or equal to about         600 W/m² and permanently activated when the intensity of the         solar exposition is lower than about 300 W/m², and     -   b) deactivated when the total exposure time (residence time) to         UV rays of the air within the plenum 16′ is greater than abut 60         seconds and permanently activated when the exposure time is less         than about 30 seconds.

It is understood that the auxiliary UV generator could take the form of any other suitable air purifying system. For instance, a chemical sterilization device or a photocatalyst device could be used in place of the UV ray generator 33. Also more than one auxiliary air sterilizing devices could be disposed between the UV exposed plenum 16′ and the conduit 35.

FIG. 10 shows another embodiment wherein the UV exposed plenum 16″ is integrated in an air recirculation system of a building in order to purify the ventilation air using solar energy before the air be returned back into the building. More particularly, the UV exposed plenum 16″ can be provided in the form of a UV transmissive conduit that could be mounted on the roof of the building or on any other suitable outdoor surface separate from the building. The conduit is provided at one end thereof with an inlet 40 for receiving contaminated air from the building. The conduit has an outlet 42 at the opposed end thereof for returning purified air into the ventilation system of the building. The wall of the conduit is at least partly made of a UV transmissive material for allowing the air to be purified by the UV rays of the sun as the air flows from inlet 40 to outlet 42. The wall of the conduit does not have to be perforated if no fresh air admission is needed. As disclosed in connection of the embodiment of FIG. 9, the system can comprise a controller 30, a fan 32, a light intensity sensor 31, an auxiliary UV generator 33, and a pair of air quality sensors 36, 37. The duplicate description of these components is herein omitted for brevity. In this example, the system is mainly used to purify/sterilize the air and not necessarily to heat the air using solar energy. Accordingly, this embodiment could be provided without any solar radiation absorber.

The integration of such a passive UV air sterilization device in the ventilation system of a building:

-   reduces or eliminates the use of chemical agents such as bioci,     germicide, viricide or antibiotic in building ventilation systems; -   reduces or eliminates recourses to artificial UV sources to treat     the air; and -   contributes to reduce building electrical consumption.

Furthermore, as can be appreciated from the above embodiments, the device can be used in several applications including:

-   -   Solar thermal air heaters     -   Solar fresh air preheater mounted on building walls or roofs     -   Hybrid solar air/water heating systems     -   Preheating of air-to-air and air-to water heat pumps     -   Transparent energy recovery device for greenhouses     -   Cooling of photovoltaic panels     -   Residential, low-cost solar preheater     -   Sterilization systems for schools, hospital, senior houses . . .

Also various apparatus can be provided downstream of the device for further processing the air. For instance, the device could be coupled to the following units:

-   -   Gas-tired make-up air unit     -   Air-based heat pump (air-to-air or air-to-water)     -   Swimming pool heat pump     -   Combustion chamber     -   Heat recovery unit     -   UV producing systems as well as other suitable air sterilizing         systems

The above described UV transmissive perforated glazing offers numerous benefits. The incoming air is admitted throughout the glazing surface, either on a large proportion of its surface or over the entire surface. Accordingly, the glazing surface remains cold so that collector top heat loss is substantially prevented. Furthermore, the air temperature inside the collector remains relatively cold, lowering heat losses through the bottom and the edges, or, if in a specific design with high residence time of the solar-heated air within the collector, the edges and bottom may be appropriately insulated. The proposed perforated transparent glazing design provides solar efficiencies at least as good as that provided by the perforated plate design at high flow rates. For lower flow rates, however, the solar efficiency remains high and by far exceeds that of opaque perforated collectors, and even exceeds that of glazed collectors, for less than half the cost. This high efficiency at low flow rates is a major advantage for air sterilizing applications where relatively long residence times are or may be needed. High efficiencies at low flow rates can be readily appreciated from FIG. 8. More particularly, it can be seen that for flow rate between 2 and 6 cfm per square foot of perforated surface, the efficiency of a perforated glazing with a black backing surface is greatly superior to that a conventional black perforated sheet metal solar collector. The difference in performance is even more noticeable for light or with color solar collectors. The perforated glazing with a white color backing surface is up to 100% more efficient than a white perforated sheet metal collector. It can also be appreciated that the difference in performance between conventional unglazed perforated collectors and the above described perforated glazed designs is even more significant at low flow rates of, for instance, 3 or 4 cfm per square foot.

It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as hereinafter defined in the Claims. 

1. A heat collector and air sterilization device comprising: a UV transmissive glazing exposed to the ambient, the UV transmissive glazing allowing at least a portion of the UV rays of the sunlight to pass therethrough, the UV transmissive glazing being spaced from a solar radiation absorbing panel and defining a plenum therewith, a plurality of perforations defined through the UV transmissive glazing for allowing outside air to flow through the UV transmissive glazing into the plenum, the perforations being distributed over a surface area of the UV transmissive glazing, the plenum having at least one outlet through which air contained in the plenum can be removed after having been warmed up and at least partly sterilized by the UV rays of the sunlight.
 2. The device defined in claim 1, wherein said solar radiation absorbing panel overlies a layer of insulation material of a building wall.
 3. The device defined in claim 1, wherein the solar radiation absorbing panel is corrugated.
 4. The device defined in claim 1, wherein the solar radiation absorbing panel has an elongated pipe-like configuration with the UV transmissive glazing running longitudinally along one side thereof.
 5. The device defined in claim 1, wherein the ratio of the perforated surface of the UV transmissive glazing over the imperforated surface of the glazing ranges from 0.5% to 10%.
 6. The device defined in claim 1, wherein the UV transmissive glazing is permeable to UV rays of the C-type, and has a UV transmittance rate that is higher than 80%.
 7. The device defined in claim 6, wherein the UV transmissive glazing is made of a material selected from the group consisting of: poly carbonates and fused silicate.
 8. The device defined in claim 7, wherein the UV transmissive glazing is made of a polycarbonate having a UV transmittance equal to or greater than 90% at wavelength comprised between between 180 nm-2.0 μm.
 9. A device for heating and sterilizing air comprising an outdoor perforated UV transmissive surface allowing at least part of the solar radiations, including UV rays, to pass therethrough, a solar radiation absorption surface located behind said outdoor perforated UV transmissive surface for absorbing the solar radiations, and a plenum defined between said outdoor perforated UV transmissive surface and said radiation absorption surface, the air flowing in the plenum absorbing heat from the radiation absorption surface while being exposed to UV rays, thereby providing for the combined heating and sterilization of the air in the plenum by solar energy.
 10. The device defined in claim 9, wherein air moving means are provided for maintaining said plenum under negative pressure.
 11. The device defined in claim 9, wherein the outdoor perforated UV transmissive surface is mounted to a building surface, the plenum being defined between the perforated UV transmissive surface and the building surface.
 12. The device defined in claim 11, wherein the building surface is a transparent membrane extending over a greenhouse skeleton structure.
 13. The device defined in claim 11, wherein the building surface forms part of the solar radiation absorption surface and is of a light color.
 14. The device defined in claim 9, wherein the solar radiation absorption surface comprises a collector panel mounted to a building surface, the outdoor perforated UV transmissive surface separating the collector panel from the ambient.
 15. A system for heating and sterilizing the air of a building comprising: at least one heat collector and air sterilization device as defined in claim 1; at least one inlet receiving air to be treated from inside the building; and at least one outlet feeding the building with heated and sterilized air.
 16. A system as defined in claim 15 further comprising: an auxiliary sterilization device selected from the group consisting of: a UV ray producing device, a chemical sterilization device and a photocatalyst device.
 17. A system as defined in claim 16, further comprising a controller for selectively actuating the auxiliary sterilization device.
 18. A system as defined in claim 16, wherein the auxiliary sterilization device is positioned downstream of said at least one heat collector and air sterilization device and upstream of the building relative to the flow of air through the system.
 19. A system as defined in claim 15 comprising at least two heat collector and air sterilization devices mounted in parallel or in series.
 20. A system as defined in claim 17, wherein the controller actuates the auxiliary sterilization device when the intensity of the solar exposition is lower than about 300 W/m² and deactivates back the auxiliary device when the intensity of the solar exposition is higher or equal to 600 W/m². 